Tone control



I April 3, 1951 G. A. BONADIO 2,547,251

TONE CONTROL Filed Sept. 8, 1947 2 Sheets-Sheet 1 10 INPUT 7 INVEN TOR. GEORGE ABONAD/O T0 6+ h m 9 r 1 flwd ATTORNEY 11 W OUTPUT April 3, 1951 G. A. BONADIO 2,547,251

TONE CONTROL Filed Sept. 8, 1947 2 Sheets-Sheet 2 Low FREQUENCY HIGH LOW FREQUENCY HIGH LOW FREQUENCY HIGH 3i INVENTOR. GEORGE Aommo ATTORNEY Patented Apr. 3, 1951 UNITED STATES PATENT 7 OFFICE TONE CONTROL George A. Bonadio, Watertown, N. Y. Application September 8, 1947, Serial No. 772,737

2 Claims.

This invention relates to a device for securing a desired pattern of frequency-energy sound response from an electrical device such as a radio receiver.

One object of this invention is to provide a device which may be easily and cheaply constructed, and may be readily inserted in already existing receivers.

Another object of this invention is to provide a device by means of which defects in the output response curve of a radio receiver may be readily corrected.

A further object of this invention is to provide a device in which several compensating circuits are combined together. in such fashion that the usually inadequate bass and treble response of a radio receiver, especially a receiver of the commonly employed type having small physical dimensions, may be independently and easily raised or corrected until the over-all response of the receiver approaches sufficiently a linear characteristic, so that the sound reproduction thereof will appear to the human ear to be greatly improved.

Still another object of thisinvention is to provide a device which will eliminate from the output of the radio receiver undesired peaks in the response curve thereof, such peaks having a marked and often irritating efiect upon the ear I of the listener.

. A still further purpose of this invention is to provide a tone correction device which will correct the acoustical output of a radio receiver at a Yet a further purpose of this invention is toprovide a tone correctin device which may be employed in connection with radio receivers, audioamplifiers, telephone systems and other sound reproducing apparatus in order to provide a tonal response which shall appear to the ear to be substantially uniform over the entire frequency range of such apparatus.

An additional object of this invention is to provide tone correction apparatus including therein adjustable elements, which apparatus-may be temporarily inserted into the electrical circuit of a .sound reproducing device, and adjustments made-until the response of the device appears uniform, such apparatus then furnishin an" indication of the correct values of the various caf pacitors and resistors which can then be per manently inserted into the circuit in order to maintain the improved response'of the device.

Sound reproducing devices, especially those of small physical size, such as radio receivers, usually deliver a sound spectrum which seems to the human ear to be extremely defective with respect to the various frequencies reproduced. This defective response usually may be analyzed as constituted by one or more of three distinct faults. These faults are: defective bass response, defective treble response and the presence of a peaked response,- usually located toward the middle of the frequency band. I I

The present invention provides simple and relatively inexpensive means for correcting all three of these response defects by simple individual adjustments incorporated Within the single device of the invention.

Many further uses and advantages of thi invention will be apparent to those skilled in the art, and from the following description and the drawings annexed to this specification.

In the drawings:

Figure 1 isa schematic representation of the device of this invention connected into an audiolustrating peak faults.

Figure 7 is a graph illustrating bass and treble V faults.

Figure 8 is a graph illustrating the corrected response curve afforded by this device.

Figure 9 is an external view of one physical embodiment of the device of this invention.

Referring now to Figure 1, reference numeral I0 indicates the input and numeral H the output tube thereof. The particular type of tube employed for these elements is unimportant and will vary according to the character of the sound reproducing device, the only requirement being that these two tubes are suited for being coupled to one another. A capacity-resistance network is here shown, but any other coupling means, suchas a transformer, may be used. Tubes lo and H are usually the last two tubes of the amplifier circuit. However, the device of this ininput grid of tube; II', this latter being grounded via a' suitable resistor M. The substitution of a transformer or other coupling device for elements l2, l3 and I4 is familiar to one skilled in the art. The device of this invention is inserted between two points, and I6 of the conductQr extending from capacitor d3 to the grid of tube Ll. The circuit of the tone corrector comprises two resistors l7 and 18, connected in series with each other between point 15 and point H5. The common connection between these two last resiStQrs is also extended to one end of a variable resistor 19, the other end of which last is connected to the ground 20, via variable capacitor :21, shunted by resistor 33.

The operation of this tone circuit device is better understood by considering the individual current paths afforded when certain elements 201? the ic'orrecter are :used individually.

Bei'em'ine' new to villieure 2,, the netwoik comprising resistors ll-l, 1.8 and i9 :is shown .connected between points 15 and it. Under these conditions, the network will present a uniform fr q e cy characteristi so that the only effect produced by resistor 1,9 :will be to lower or aise the response curve substantially uniformly at all portions thereof,

Referring now to Figure '3, variable capacitor ii is substituted for resistor 1-9 oiiFigurei2. Under these conditions, the bypass or shunting effeet of capacitor 2 will-increase with frequency, so that the response curve will fall on substantially lineanly as the frequency rises, whereby adjustment oi this capacitor will efiectively allow the bass tones to be magnified in 3181211111011 to the treble tones, resistor 33 limiting this efiect.

Referring now to Figure 4, variable capacitor 23 will exhibit ,a vrising :freqllency characteristic with respect to the transmission f energy be tween points 55 and it, thus imparting arising characteristic to response curve. Therefore, an increase in capacity of element 2.3 will cause an increase in the treble response .of the am-plifler relative to the bass response thereof.

Referring again to Figure 1, it can Joe seen that this circuit embedies a combination cf the individual circuits as shown in Figures 12,13 and 4.

it will therefore be apparent to one :skilled in the art that the adjustments of elements 19,

2t, 33 and 23 will provide ,means dior separately increasing or decreasing bass tones, treble tones and the over-all level'oi response .of the ampliher at will, thereby allowing at least an approximate equalization of the entire response curve thereof.

Reierring now to Figure 5, this illustrates a frequency response curve characterized :by .an undesired peak. This is often found in small radio receivers, and gives rise to irritating psychological efiects upon thelistener, especially when the peak falls the middle of .the sound spectrum, so that it is frequently encountered.

Figure 6 shows a curve of character just opposite to that of Figure '5. In this case, certain frequencies are partly suppressed, but the .ear does not react to such loss vof frequencies, in a manner to cause irritation to the listener. Therefore if we are able to suppress undesired peaks, even if byso doing we icause adepression in the response curve, we :ean yet avoid :the irritating efifect just described.

Figure 7 .shows a curve characteristic of vmany small radio receivers, in which the main-response is in the middle of the spectrum, while :both the low and the high frequenciesare greatly reduced. Figure .8 is an illustrative curve of the type.

whiohmay be ;secured by empley ng the device of the instant invention. In this case, adjustment of resistor l9 aids in reducing any midpeak, while capacitors 2i and 23 are adjusted to raise the bassand the treblerespectively. There- .by a curvesuoh as that shown in Figure 7 may be transformed into the form of Figure 8. The middle portion of the spectrum is here unchanged from that shown in Figure 7, where a peaked center gradually falls ofi on either side. Capacitor 2], when at a maximum, effectively magnifies the bass "relatively to the treble, as already .ezcplained the description of Figure 3. Similarly, capacitor 23 amplifies the treble relatively to the bass, as explained in discussing Figure 4. While such curve is not strictly linear, yet the peaks are so relatively slight, and so evenly spaced along the spectrum, that "to the :average uncritical ear the response will appear to :be substantially uniform over the entire range of the radio :receiver. It has been found by trial that ptoyidcd a minimum of -three,;not toosharp, peaks .are secured, :and provided that .arll .the peaks are of about identical amplitude, the result will be satisfactory, and the output of the receiver will be made to approach, as apper-' ceived :by the listener, that of a receiver .possessed or" much higher fidelity response, while the cost of securing this result will be much less than is required for the construction :of such correct the tone of a given receiver, especially For .thispur a receiver already in actual use. pose, it is possible to so embody this invention as to incorporate the circuits thereof in the form of a portable unit, which may .be .arrangedso as to ,allow connection thereof into an :already ex isting receiver without the need of tools, :or of dismantling the receiver in order to make such interconnection.

fInjFi'gu-re 9 is shown the external appearance of such a nmtable embodiment of this invention- An adaptor, or janytype suitable for the second of the two tubes hetweenwhich-the device is to be inserted in the euclioirequency circuit of the. receirer, and provided with the conventional prong-receiving apertures 25 and prongs 25, is connected by a multi-conductor cable .26 .to a cabinet 2-1, .upon the outer face of which latter are situated ,a plurality of control knobs :or the like, 28, :29, 30, 3! and 32 Each of these knobs controls the operation, within the cabinet, of a corresponding electrical element, which elements are designed either to insert v:or remove the tone I cor-rector from the amplifier circuit, or to .vary

the 'valuesof the different capacitors and re-- sistors employed to constitute the tone corrective circuits of this invention. For example,

knob 2,8 may control the fon-ofi switch, ,knobs 29 and .39 the two variable capacitors, which may conveniently be made variable in steps, rather than continuously, and knob 3 I may control the variable resistor 19. It has sometimes been found of advantage also to be able to change the value of resistor ill, for example by shunting it with another resistor of variable value.

Knob .32 may control such adjusting resistor, or resistor 33. However, this last control may-om tionally .be omitted, :as it is not essential to the fu-nctiouingiof this invention.

In the operation of the embodiment of this invention shown in Figure 9, it is preferred that the various knobs be each provided with an indicating scale, the indicia of which latter correspond with the units representing the particular electrical values presented by each resistor or capacitoractually connected in circuit at any given instant by the operation of a specific knob. After the correct electrical values for each component of the tone corrector have been ascertained by temporarily connecting into the receiver circuit this portable tone corrective unit, and adjusting the knobs until the desired effects are obtained, it is then possible to remove the unit from the circuit and permanently to substitute therefor an assembly of fixed capacitors and resistors, each respectively having an electrical value corresponding to the value indicated by the particular knob of the portable unit governing such resistor or capacitor. Such permanent unit may, of course, be made of a size and'cost very much less than that of the portable unit, which must be provided with variable components, occupying a much greater space.

The adjustment of the various elements of this device in order most expeditiously to secure the desired results has been found to be advantageously performed as follows, such particular mode of operation being understood, however, to be merely illustrative and not limiting.

Resistor I9 is reduced to approximately zero, and capacitors 2i and 23 are separately adjusted until the bass and treble response are each raised in value to give respectively two of the three peaks of Figure 8. Resistor I9 is then increased so as to raise the mid-frequency response and thereby to give the slight middle peak shown in Figure 8. These adjustments may most precisely be made by using a variable audiofrequency generator and an output meter, but in practice it has been found that adjustments to yield acoustically pleasant results may be made simply by listening to a steadily received signal, the audiofrequencies of which cover the entire spectrum, e. g. the background noise level, balancing treble and bass as above described, and finally adjusting mid-frequencies to match. I

While not limiting this invention, but merely by way of example, the following values of the various components of this tone corrector have been found to give good results with tubes and power outputs usually encountered in the case of the average radio receiver in domestic use.

Resistor I 9 may be as low as 100,000 ohms maximum, but it is preferred to extend the range thereof up to a maximum of 500,000 ohms. Capacitor 2| may extend from 0.002 to 0.1 mfd., capacitor 23 from 0.00004 to 0.002 mid, anclresistors I! and I8 may be of about 100,000 ohms each. All these component elements may be of commercial types, since a tolerance of variation of at least 5% in electrical values is allowable in ordinary practice. If capacitor 2| be switch controlled, such switch should be of the continuous or non-breaking contact type to avoid disturbing blasts of sound while adjusting. For a similar reason any switch used to control capacitor 23 should avoid contacting two points simultane ously. Switches for securing both these results are well known in the art and form no essential part of the instant invention.

It will be evident to those skilled in the art that while the above description has shown the application of this invention to audiofrequency channels, it is readily possible to apply the same fundamental circuits to the control of high or intermediate frequencies, by making such easily computed changes in the electrical values of the various components as will suit them for the particular frequencies employed.

While there have been shown and described certain embodiments and uses of this present invention, it is to be understood that many other forms and uses thereof will be apparent to those skilled in the art, and therefore this invention is limited only by the scope of the hereunto appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. For use with a multi-tube electronic amplifier, a tone corrective device, means for connecting said device between the output anode circult of a predetermined tube and the grid input circuit of the next subsequent tube of said amplifier, including two resistors connected in series, a variable capacitor shunting both said resistors, a third variable resistor connected at one end to the connection between said two first resistors, and a second variable capacitor connected at one side to the other end of said third resistor and connected at the other side to the common input and output cathode portion of the circuit of said amplifier, said connection being made to at least one of said tubes, said device also including an additional variable resistor connected in shunt to said second variable capacitor, whereby the voltage across said second variable capacitor can be limited.

2. An adjustable tone corrective device for insertion in the input circuit of an electronic amplifier tube having a cathode, grid and anode, ineluding a first current path comprising in series a variable and a fixed resistor and a variable capacitor in shunt with said two resistors, a second current path comprising a second variable resistor and a second Variable capacitor in series with one another, connections placing said first current path in series with the grid of said tube, and other connections placing said second current path effectively in shunt between the connection point of said first fixed and variable resistors and the common input and output cathode portion of the circuit of said amplifier, said portion being connected to the cathode of said tube, said first resistor remaining substantially constant at all times, so as to pass current of medium frequency without change, and said first capacitor forming the means whereby the amount of higher frequency current relative to said medium frequency current may be adjusted.

GEORGE A. BONADIO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,949,634 Simpson Mar. 6, 1934 2,069,853 Schade Feb. 9, 1937 2,192,959 Ballard Mar. 12, 1940 2,253,186 Loye et a1. Aug. 19, 1941 

